This application generally relates to mechanical systems which generate vibrations, such as cryocoolers, and more particularly, to reducing and controlling vibrations thereof.
Linear cryocoolers generate significant force and disturbances during operation. This may even occur for those cryocoolers designed to be inherently balanced. The disturbances primarily result from slight imperfections in the internal moving mechanisms and asymmetries in internal gas flows therein. These can negatively impact the performance of systems into which the cryocooler is integrated. One such system, is a cooled infrared (IR) camera used in a thermal weapon sight or satellite-based missile detection system. Mechanical disturbances generated by the cryocooler during operation can cause high-frequency movement or “jitter” in the sensor's optical components and/or detector, leading to unacceptable levels of performance degradation.
The conventional method for handling vibrations is to employ an active vibration reduction system. Such systems utilize cryocooler-mounted sensors to sample the disturbance output of the cryocooler, after which the data is processed and used to generate a precisely-tuned signal that is fed back into the cryocooler drive waveform(s). This signal causes motor forces to be generated that (at least partially) counteract the originally-sample disturbance, resulting in lower overall disturbance output. Typically, these systems are iterative such that the cancellation signal is formed slowly (i.e., relative to the cryocooler operational frequency), with successive iterations resulting in progressively lower disturbance output.
Processing the disturbance in such a system involves performing frequency analysis on the data (for instance, fast Fourier transform (FFT)) or convolution-based analysis. In this way, the time-domain data is decomposed into a series of individual-frequency constituents, and this frequency-domain data is used to individually generate cancellation waveforms for each specific frequency of interest. For typical cryocoolers, the frequencies of interest are integer multiples of the operating frequency because this is where the majority of disturbances occur.
While these frequency-based analysis algorithms may be accurate, they require a significant amount of processing power in order to perform the algorithm processing at a reasonable rate. For very high-performance cryocooler systems, such as those used in space applications, this is often not an issue because system cost and complexity are typically considered secondary to achieving the highest performance possible. On the other hand, lower-cost cryocooler systems, such as those used in tactical applications, typically forgo active vibration reduction in order to minimize system cost and complexity.
As such, an improved vibration reduction methodology is desired which requires less processing power.